Rotation shaft seal

ABSTRACT

A rotation shaft seal provided with a rubber sealing portion which contacts a surface of a rotation shaft and an outer case to which the rubber sealing portion is unitedly fixed. The outer case has an inner brim portion on an inner end portion on a sealed fluid side. The inner brim portion is covered by the rubber sealing portion. A sliding portion is disposed on an axis-orthogonal face including the inner brim portion.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. application Ser.No. 10/849,876, filed May 21, 2004, now U.S. Pat. No. 7,134,670 andclaims the right of priority under 35 U.S.C. §119 based on JapanesePatent Application No. 2003-152361 filed on May 29, 2003 and JapanesePatent Application No. 2003-165544 filed on Jun. 10, 2003, which ishereby incorporated by reference herein in its entirety as if fully setforth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a rotation shaft seal, especially, a rotationshaft seal used to seal high-pressure fluid such as gas.

2. Description of the Related Art

Conventionally, a rotation shaft seal 31 as shown in FIG. 16, having across-sectional configuration of a rubber lip 33 touching a surface of arotation shaft 32 extends from an outer case 34 toward a sealed fluidside C as to be approximately L-shaped, is used (refer to Japanesepatent provisional publication No. 2003-97723, for example). That is tosay, the rotation shaft seal 31 is provided with the outer case 34having an inner brim 36 on an end portion of the sealed fluid side C, arubber member 37 is united with the outer case 34 by adhesive or brazingas to surround the inner brim 36 of the outer case 34 and cover aperipheral face of the outer case 34. And, a supporting metal 38 havingan L-shaped cross-sectional configuration supports the rubber lip 33 ona low pressure side E and the inner peripheral face side (on a back),and a lip end portion 33 a is on a position on an axis direction greatlyapart from an axis-orthogonal face P₀ including the inner brim 36 of theouter case 34. That is to say, a sliding portion S₀ exists on a positionon an axis direction greatly apart from the axis-orthogonal face P₀including the inner brim 36, and the rubber lip 33 is in a configurationhaving a cylindrical extension 33 c supported by a cylinder portion 38 aof the supporting metal 38.

And, conventionally, in this kind of rotation shaft seals, efforts havebeen paid in design and production to make the end portion 33 a of thelip 33, namely, the sliding portion S₀, uniformly sliding on therotation shaft 32 in the peripheral direction. Therefore, the cylinderportion 38 a of the supporting metal 38 is consequently composed of asmooth cylindrical wall portion to have an accurate circular crosssection.

In a high-pressure state in which high pressure works on a sealed fluidchamber 39, as shown in FIG. 3B, the cylindrical extension 33 c of therubber lip 33 is compressed and deformed, rubber flows (moves) in anarrow F direction for the supporting metal 38 stopping the rubber, thelip end portion 33 a also receives the pressure from the sealed fluidside C, and the rubber looses flexibility because inner stress of therubber concentrates right on the sliding portion S₀. Large contactpressure (pressure) P as shown in FIG. 3B is generated on the slidingportion S₀ because the contact pressure is generated by pressing to therotation shaft seal 32 through the rubber of the area on which the innerstress concentrates. And, sealed fluid (lubricant oil included in thefluid) hardly intrudes on the surface between the rotation shaft 32 andthe sliding portion S₀ because of the above-mentioned large contactpressure P, and abrasion on the sliding portion S₀ of the lip endportion 33 a is promoted thereby. Then, the abrasion proceeds as to biteinto the sliding portion S₀, tightness (sealability) of the seal israpidly deteriorated, and outer leak of the fluid is generated.

And, in FIGS. 9C and 10C showing the conventional example, the lip endportion 33 a (the sliding portion S₀) contacts the whole periphery(360°) of the rotation shaft 32 uniformly with large contact pressure Pas shown in FIG. 10C when the high pressure works on the sealed fluidchamber 39. The lubricant oil in the sealed fluid hardly intrudes on(being induced to) the surface between the rotation shaft 32 and thesliding portion S₀, abrasion on the sliding portion S₀ of the lip endportion 33 a is promoted, the abrasion proceeds as to bite into thesliding portion S₀, tightness (sealability) of the seal is rapidlydeteriorated, and outer leak of the fluid is generated. In other words,under a high-pressure circumstance, adding to the strong pressing of theend portion 33 a of the rubber lip 33 to the rotation shaft 32, the endportion 33 a is uniformly pressed to the whole periphery of the rotationshaft 32, the lubricant oil in the fluid such as a cooling medium cannot intrude on the surface of the sliding portion S₀ and the rotationshaft 32, frictional resistance is increased, heat is generated, and thesliding portion S₀ is rapidly abraded.

It is therefore an object of the present invention to provide a rotationshaft seal, with which the contact pressure of the rubber sealingportion on the contact portion on the rotation shaft is restricted asnot to be excessive, having long life for sealing high-pressure gas.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described with reference to theaccompanying drawings in which:

FIG. 1 is a cross-sectional view of a principal portion showing anembodiment of the present invention;

FIGS. 2A and 2B are enlarged explanatory comparison views ofconfigurations of the embodiment of the present invention and aconventional example;

FIGS. 3A and 3B are explanatory views to compare configurations andworking of the present invention and the conventional example;

FIG. 4 is a cross-sectional view of a principal portion showing anotherembodiment;

FIGS. 5A and 5B are explanatory comparison views of differentembodiments of the present invention;

FIGS. 6A and 6B are explanatory comparison views of differentembodiments of the present invention;

FIG. 7 is a graph showing change in maximum contact pressure to fluidpressure in the present invention and the conventional example;

FIG. 8A is a cross-sectional side view of a principal portion showingstill another embodiment of the present invention;

FIG. 8B is a rear view of a principal portion showing still anotherembodiment of the present invention;

FIGS. 9A through 9C are enlarged explanatory comparison views ofconfigurations of still another embodiment of the present invention andthe conventional example;

FIGS. 10A through 10C are explanatory views to compare configurationsand working of the present invention and the conventional example;

FIGS. 11A and 11B are explanatory views of further embodiments of thepresent invention;

FIG. 12A is a cross-sectional side view of a principal portion showingstill further embodiment of the present invention;

FIG. 12B is a rear view of a principal portion showing still furtherembodiment of the present invention;

FIGS. 13A and 13B are rear views of principal portions of furtherembodiments of the present invention;

FIG. 14A is a cross-sectional side view of a principal portion showingstill further embodiment of the present invention;

FIG. 14B is a rear view of a principal portion showing still furtherembodiment of the present invention;

FIG. 15A is a cross-sectional side view of a principal portion showingfurther embodiment of the present invention;

FIGS. 15B through 15D are cross-sectional views of principal portionsshowing further embodiments of the present invention; and

FIG. 16 is a cross-sectional view of a principal portion showing aconventional example.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be describedwith reference to the accompanying drawings.

FIG. 1 shows an embodiment of the present invention. This rotation shaftseal is, for example, used for sealing high-pressure cooling media on asealed fluid chamber 21 side. A half cross section of the rotation shaftseal is shown in FIG. 1, solid lines show a free state, namely,unattached state, and parts of the seal are elastically deformed in anattached state in which the seal is disposed between a rotation shaft 20and a housing 22.

In FIG. 1, a mark 1 represents an outer case of metal having inner brimportions 2 and 3. A sealing portion 5 of rubber is unitedly fixed to aperipheral face of a cylindrical wall portion 4 of the outer case 1 andboth faces of the inner brim portion 2 on a sealed fluid side C (thesealed fluid chamber 21 side) by adhesion, welding, or brazing. A sealelement 7 having a spiral groove 6 is disposed on an opposite side (alow pressure side or an atmosphere side) Z to the sealing portion 5. Theseal element 7 is preferably made of fluororesin such as PTFE.

A mark 8 represents a supporting metal having I-shaped cross section.The supporting metal 8 of a circular flat plate is fit as a peripheraledge portion 8 a contacts the inner peripheral face of the cylindricalwall portion 4 of the outer case 1. The supporting metal 8, a firstinner case 9, a second inner case 10, the seal element 7, and an innermember 11 are serially disposed to be fit between the inner brimportions 2 and 3.

The rubber sealing portion 5, unitedly fixed to the outer case 1, isprovided with a cylindrical cover portion 5 a of which peripheral faceis formed undulate (in the free state) to elastically contact the innerperipheral face of the housing 22 to seal, and an axis-orthogonal wallportion 5 b extended in an inner radial direction, having an inner brimcover portion having U-shaped cross section to cover the both sides ofthe inner brim portion 2 on an upper part, and a sliding portion 23 onan inner peripheral end.

That is to say, the rubber sealing portion 5 is provided with theaxis-orthogonal wall portion 5 b at right angles with an axis L of therotation shaft 20 (the rotation shaft seal), and the sliding portion 23having a rounded (R-shaped) portion is composed of the inner peripheralend of the axis-orthogonal wall portion 5 b. The supporting metal 8 ofcircular flat plate supports (presses) the axis-orthogonal wall portion5 b on the low pressure side, namely, the opposite side Z.

And, the axis-orthogonal wall portion 5 b of the rubber sealing portion5 has a circular concave groove 24 on a back face corresponding(pressed) to the supporting metal 8.

As described later, the concave groove 24 absorbs and/or cuts a flow ofcompressed rubber of the axis-orthogonal wall portion 5 b in the innerradial direction (inward in radius).

In other words, the outer case 1 has the inner brim portion 2 on theinner end portion on the sealed fluid side C, and the sliding portion 23is disposed on an axis-orthogonal face P₀ including the inner brimportion 2.

That is to say, the inner brim portion 2 has a (small) thickness, pluralaxis-orthogonal faces P₀ exist on positions in the axis direction forthe (small) thickness. The position of the sliding portion 23 in theaxis direction is disposed on at least one of the orthogonal faces P₀.The position of the sliding portion 23 in the axis direction is definedas a position of a center of gravity G (refer to FIG. 3A) of contactpressure P when sliding on the rotation shaft 20 under the maximumoperation pressure.

Although not shown in Figures, it is also preferable to dispose theposition of the sliding portion 23 in the axis direction near theaxis-orthogonal face P₀. The word “near” means deviation within 5 timesof the thickness of the inner brim portion 2.

It is also possible to restate that the position of the sliding portion23 in the axis direction is disposed within a width dimension M of theouter case 1 in the axis direction. The width dimension M in the axisdirection is defined as a dimension in which a thickness dimension T₁₇of a rubber covering layer 17 covering the inner brim portion 2 on thesealed fluid side C is included (added to). Specifically, the positionof the sliding portion 23 is disposed within a thickness dimension ofthe axis-orthogonal wall portion 5 b of the rubber sealing portion 5covering the inner brim portion 2. With this construction, positionsreceiving the pressure from the sealed fluid side C do not exist on anouter side in the radial direction to the center of gravity G ofdistribution of the contact pressure P when the sliding portion 23receives the pressure. It is clearly shown when FIG. 3A is compared withthe conventional example of FIG. 3B.

Next, FIG. 4 shows a second embodiment. In FIG. 4, explanation of thesame marks, showing similar constructions as in FIG. 1, is omitted. Adifference is that the concave groove 24 in FIG. 1 is omitted in FIG. 4(functional differences will be described later with FIGS. 5A through6B).

To describe additionally the configuration of the axis-orthogonal wallportion 5 b of the rubber sealing portion 5 in FIGS. 1 and 4, thesliding portion 23 is a convex arc in the free state (unattached state),and the convex arc continues to a contact portion with the supportingmetal 8. However, a bill-shaped (triangle) protruding portion 13 isformed on the sealed fluid side C.

In other words, although most of the end face 14 of the axis-orthogonalwall portion 5 b on the sealed fluid chamber 21 side is flat (of flatface), the end face 14 has the protruding portion 13 formed as to be abill-shaped (triangle) protrusion.

When the sliding portion 23 is abraded by sliding on the rotation shaft20, rubber is (newly) sent from the protruding portion 13 by fluidpressure. That is to say, rubber is newly supplied by the protrudingportion 13 in abrasion to keep the sliding state of the sliding portion23 on the rotation shaft 20 to maintain the sealability.

FIGS. 2A through 3B are showing a principal portion of the embodimentshown in FIG. 1 and the conventional example shown in FIG. 16 side byside. FIGS. 2A and 2B are for comparison in the free state, and FIGS. 3Aand 3B are for comparison in pressure-receiving (operational) state inwhich the fluid pressure works.

As clearly shown by FIGS. 2A through 3B, the present inventioncompletely lacks the cylindrical extension 33 c (parallel to the axis L)and the cylinder portion (cylindrical supporting portion), whenhigh-pressure gas such as CO₂ works (in pressure-receiving state), thepressure does not directly work (have influence) on the sliding portion23. Therefore, although high specific pressure is generated in theconventional seal as a diagram of contact pressure distribution shown inFIG. 3B, specific pressure is reduced and pressure distribution is madegentle in the present invention as a diagram 15 of contact pressuredistribution shown in FIG. 3A. In FIGS. 3A and 3B, two-dot broken linesshow the free state, and solid lines show the pressure-receiving statein which fluid pressure of 6 MPa works.

Conducting an analysis of the contact pressure with FEM, when the fluidpressure is 6 MPa, the maximum contact pressure, reached approximately11 MPa in the conventional example of FIG. 3B, was about 8 MPa, reducedby about 3 MPa in the present invention of FIG. 3A. And, although notshown in Figures, analysis of inner stress distribution of the rubber byFEM revealed that the absolute value of high stress area, whichconcentrates around the concave groove 24, is small near the slidingportion 23 and dispersed within a large area. (On the contrary, the highstress area concentrates on the sliding portion S₀ in the conventionalexample of FIG. 3B.)

Working (action) of the seal relating to the present invention iscompletely different from that of the conventional example (of FIG. 3B)in a point that the contact pressure is obtained by self-sealing effectlike ordinary O-rings. That is to say, in the conventional example, thefluid pressure in the inner radial direction directly works on the lipend portion 33 a (greatly) extended to the sealed fluid side C and thepressing force by the flow of rubber in the arrow F direction is addedto raise the contact pressure P of the sliding portion S₀. In therotation shaft seal relating to the present invention, the fluidpressure works firstly on the end face 14 of the axis-orthogonal wallportion 5 b as compression force to the supporting metal 8 on the backside because the working direction is parallel to the axis L, the rubberis compressed, deformed, and moved in the inner radial direction toindirectly push the sliding portion 23 to generate sealing force(sealability). The working (action) corresponds to self-sealing effectof O-rings. Therefore, excessively strong pressing force is preventedfrom working, the specific pressure is made relatively low as shown witha gentle hill of the diagram 15 of contact-pressure distribution in FIG.3A, and preferable improvement of durability is made possible thereby.

Further, in FIGS. 1, 2A, and 3A, the concave groove 24 absorbs therubber moving in the inner radial direction (the concave groove 24 asshown with the two-dot broken line is diminished as shown with the solidline) and/or cuts the movement of the rubber in the inner radialdirection to reduce the influence to the increase of the contactpressure on the sliding portion 23.

The working effect of the concave groove is clearly shown by FIGS. 5Athrough 6B. FIGS. 5A and 6A correspond to the case having the concavegroove 24 (corresponding to FIG. 1), FIGS. 5B and 6B correspond to thecase without the concave groove 24 (corresponding to FIG. 4), and thecontact pressure is analysed by FEM analysis to draw diagrams 15 of thecontact pressure distribution. The fluid pressure is 0 in FIGS. 5A and5B, and 6 MPa in FIGS. 6A and 6B. In FIGS. 5A and 5B, when interferenceis 0.6 mm, the maximum contact pressure P is more than 3 MPa without theconcave groove 24 in FIG. 5B, and approximately 2 MPa with the concavegroove 24 in FIG. 5A, reduced by about 1 MPa. And, when the fluidpressure of 6 MPa works (pressure-loading state), the maximum contactpressure P is 9.6 MPa in FIG. 6B, and 8.5 MPa in FIG. 6A, about 1 MPalower.

Next, FIG. 7 is a graph showing “the fluid pressure to the maximumcontact pressure” relationship in which the fluid pressure (loadedpressure) is on the axis of abscissae and the maximum contact pressure,namely, the maximum value of the contact pressure on the rotation shaft,is shown on the axis of ordinates. The conventional example is shownwith circles and the present invention is shown with triangles, both areanalysed by FEM analysis, and actually-measured value of an O-ring isshown with rhombuses.

As shown in FIG. 7, sufficient sealability (tightness) is obtained bythe O-ring with the maximum contact pressure of 8 MPa when the fluidpressure is 6 MPa, and the product of the present invention (triangles),showing characteristics very similar to that of the O-ring, hassufficient sealability and durability. On the contrary, the maximumcontact pressure becomes excessive of 11 MPa when the fluid pressure is6 MPa in the conventional example (circles) which may have problems suchas early abrasion.

In the present invention, not restricted to the embodiment above, arubber lip portion may be disposed on the low-pressure side independentfrom the rubber sealing portion 5, number of the seal elements 7 may be2 or more, the seal element 7 may be omitted, and the configuration ofthe supporting metal 8, number and configurations of the inner cases 9and 10 and the inner member 11 may be changed.

FIGS. 8A and 8B show another embodiment of the present invention. FIG.8A shows a longitudinal cross section of a principal portion, and FIG.8B is a simplified explanatory view of construction in which theprincipal portion is observed in the axis L direction. This rotationshaft seal is, for example, to seal fluid such as high pressure coolingmedium on the sealed fluid chamber 21 side. A half cross section of therotation shaft seal is shown in FIG. 8A, solid lines show a free state,namely, unattached state, and the rotation shaft 20 and the housing(casing) 22 are shown with two-dot broken lines. Parts of the seal areelastically deformed in an attached state in which the seal is disposedbetween the rotation shaft 20 and the housing 22.

In FIGS. 8A and 8B, although description of the members of the samemarks as in FIG. 1, similarly constructed as in FIG. 1, is omitted, theaxis-orthogonal wall portion 5 b of the rubber sealing portion 5 has aring concave groove 24 on a back face corresponding (pressed) to thesupporting metal 8 in FIG. 8A. FIG. 8B is a rear view showing an exampleof the ring concave groove 24 (observed in the axis L direction).

As described later, the ring concave groove 24 absorbs and/or cuts aflow of compressed rubber of the axis-orthogonal wall portion 5 b in theinner radial direction (inward in radius).

In other words, the outer case 1 has the inner brim portion 2 on theinner end portion on the sealed fluid side C, and the sliding portion 23is disposed on an axis-orthogonal face P₀ including the inner brimportion 2.

That is to say, the inner brim portion 2 has a (small) thickness, pluralaxis-orthogonal faces P₀ exist on positions in the axis direction forthe (small) thickness. The position of the sliding portion 23 in theaxis direction is disposed on at least one of the orthogonal faces P₀.The position of the sliding portion 23 in the axis direction is definedas a position of a center of gravity G (refer to FIG. 10A) of contactpressure P when sliding on the rotation shaft 20 under the maximumoperation pressure.

Although not shown in Figures, it is also preferable to dispose theposition of the sliding portion 23 in the axis direction near theaxis-orthogonal face P₀. The word “near” means deviation within 5 timesof the thickness of the inner brim portion 2.

It is also possible to restate that the position of the sliding portion23 in the axis direction is disposed within a width dimension M of theouter case 1 in the axis direction. The width dimension M in the axisdirection is defined as a dimension in which a thickness dimension T₁₇of a rubber covering layer 17 covering the inner brim portion 2 on thesealed fluid side C is included (added to). Specifically, the positionof the sliding portion 23 is disposed within a thickness dimension ofthe axis-orthogonal wall portion 5 b of the rubber sealing portion 5covering the inner brim portion 2. With this construction, positionsreceiving the pressure from the sealed fluid side C do not exist on anouter side in the radial direction to the center of gravity G ofdistribution of the contact pressure P when the sliding portion 23receives the pressure. It is clearly shown when FIG. 10A is comparedwith the conventional example of FIG. 10C.

Next, a remarkable characteristic of the present invention is described.In FIGS. 8A through 10B, the ring concave groove 24 is set to have depthdimensions changing in peripheral direction to make the contact pressureP of the sliding portion 23 on the rotation shaft 20 uneven (ununiform)in the peripheral direction. In FIG. 8A, a solid line shows a portion D₁of shallow (small) depth dimension, and a broken line shows a portion D₂of deep (large) depth dimension. In the example of FIG. 8B, portions D₁of shallow depth dimension of which central angle α is about 60° andportions D₂ of deep depth dimension of which central angle β is about60° are disposed in turn. It is possible to set α>β, or oppositely α<β.The contact pressure P is small with the portions D₂ of deep depthdimension as in FIG. 10B, the lubricant oil in the fluid is easilyinduced and spread over the entire periphery of the sliding portion 23to restrict the abrasion of rubber.

To describe additionally the configuration of the axis-orthogonal wallportion 5 b of the rubber sealing portion 5 in FIGS. 8A through 9B, thesliding portion 23 is a convex arc in the free state (unattached state),and the convex arc continues to a contact portion with the supportingmetal 8. However, a bill-shaped (triangle) protruding portion 13 isformed on the sealed fluid side C.

In other words, although most of the end face 14 of the axis-orthogonalwall portion 5 b on the sealed fluid chamber 21 side is flat (of flatface), the end face 14 has the protruding portion 13 formed as to be abill-shaped (triangle) protrusion.

When the sliding portion 23 is abraded by sliding on the rotation shaft20, rubber is (newly) sent from the protruding portion 13 by fluidpressure. That is to say, rubber is newly supplied by the protrudingportion 13 in abrasion to keep the sliding state of the sliding portion23 on the rotation shaft 20 to maintain the sealability.

FIGS. 9A through 10C are showing a principal portion of the embodimentshown in FIGS. 8A and 8B and the conventional example side by side.FIGS. 9A through 9C are for comparison in the free state, and FIGS. 10Athrough 10C are for comparison in pressure-receiving (operational) statein which the fluid pressure works. And, FIGS. 9A and 10A show a crosssection of the portion D₁ of shallow depth dimension, FIGS. 9B and 10Bshow a cross section of the portion D₂ of deep depth dimension, andFIGS. 9C and 10C show the conventional example.

As clearly shown by FIGS. 9A through 10C, the embodiment of the presentinvention shown in FIG. 8A completely lacks the cylindrical extension 33c (parallel to the axis L) and the cylinder portion (cylindricalsupporting portion) 38 a, when high-pressure gas such as CO₂ works (inpressure-receiving state), the pressure does not directly work (haveinfluence) on the sliding portion 23. Therefore, although high specificpressure is generated in the conventional seal as a diagram of contactpressure distribution shown in FIG. 10C, specific pressure is reducedand pressure distribution is made gentle in the embodiment of thepresent invention as diagrams 15 of contact pressure distribution shownin FIGS. 10A and 10B. In FIGS. 10A through 10C, two-dot broken linesshow the free state, and solid lines show the pressure-receiving statein which fluid pressure of 6 MPa works.

Conducting an analysis of the contact pressure with FEM, when the fluidpressure is 6 MPa, the maximum contact pressure, reached approximately11 MPa in the conventional example of FIG. 10C, was about 8 MPa, reducedby about 3 MPa in the present invention of FIG. 10A. And, although notshown in Figures, analysis of inner stress distribution of the rubber byFEM revealed that the absolute value of high stress area, whichconcentrates around the concave groove 24, is small near the slidingportion 23 and dispersed within a large area. (On the contrary, the highstress area concentrates on the sliding portion S₀ in the conventionalexample of FIG. 10C.)

Working (action) of the rotation shaft seal relating to the embodimentof the present invention shown in FIGS. 8A, 9A, 9B, 10A, and 10B (andlater-described other embodiments shown in FIGS. 12A through 14B) iscompletely different from that of the conventional example (of FIG. 10C)in a point that the contact pressure is obtained by self-sealing effectlike ordinary O-rings. That is to say, in the conventional example, thefluid pressure in the inner radial direction directly works on the lipend portion 33 a (greatly) extended to the sealed fluid side C and thepressing force by the flow of rubber in the arrow F direction is addedto raise the contact pressure P of the sliding portion S₀. In theembodiment of the seal relating to the present invention, the fluidpressure works firstly on the end face 14 of the axis-orthogonal wallportion 5 b as compression force to the axis-orthogonal supporting metal8 on the back side because the working direction is parallel to the axisL, the rubber is compressed, deformed, and moved in the inner radialdirection to indirectly push the sliding portion 23 to generate sealingforce (sealability). The working (action) corresponds to self-sealingeffect of O-rings. Therefore, excessively strong pressing force isprevented from working, the specific pressure is made relatively low asshown with gentle hills of the diagrams 15 of contact-pressuredistribution in FIGS. 10A and 10B, and preferable improvement ofdurability is made possible thereby.

Further, the concave groove 24 absorbs the rubber moving in the innerradial direction (the concave groove 24 as shown with the two-dot brokenline is diminished as shown with the solid line) and/or cuts themovement of the rubber in the inner radial direction to reduce theinfluence to the increase of the contact pressure on the sliding portion23.

The working effect of the concave groove is clearly shown by FIGS. 11Aand 11B. FIG. 11A corresponds to the case having the concave groove 24(corresponding to FIG. 8A), FIG. 11B corresponds to the case without theconcave groove 24, and the contact pressure is analysed by FEM analysisto draw diagrams 15 of the contact pressure distribution. The fluidpressure is 6 MPa in FIGS. 11A and 11B. When interference is 0.6 mm andthe fluid pressure is 0, the maximum contact pressure P is more than 3MPa without the concave groove 24, and approximately 2 MPa with theconcave groove 24, reduced by about 1 MPa. And, when the fluid pressureof 6 MPa works (pressure-loading state), the maximum contact pressure Pis 9.6 MPa in FIG. 11B, and 8.5 MPa in FIG. 11A, about 1 MPa lower.

Next, FIGS. 12A and 12B show another embodiment. FIG. 12A is alongitudinal cross section of a principal portion, FIG. 12B is a (rear)view of the ring concave portion 24 observed in a direction parallel tothe axis L, and positions in the radial direction of the concave groove24 are changed in turn for predetermined central angles α and β.

That is to say, although the members of the same marks are similarlyconstructed to FIG. 8A, following points are different. A solid lineshows an arc portion D₃ on which the position of the concave groove 24in the radial direction is near the axis L, a broken line shows an arcportion D₄ on which the position of the concave groove 24 in the radialdirection is far from the axis L, and the arc portions D₃ and D₄ aredisposed in turn with central angles α and β of about 60° for example.In other words, the arc portion D₃ of the central angle α has a smallradius from the axis, and the arc portion D₄ of the central angle β,shown with hatching in FIG. 12B, has a large radius from the axis. Theboth arc portions D₃ and D₄ are connected through staged portions toform the concave groove 24 ring shaped as a whole. It is possible to setthe number of each of the arc portions D₃ and D₄, 4 or more, α>β, orα<β. The contact pressure P of the sliding portion 23 is low with thearc portion D₃ of small radius dimension from the axis, the lubricantoil in the fluid is easily induced and spread over the entire peripheryof the sliding portion 23 to restrict the abrasion of rubber.

As described above, in the embodiment of FIGS. 12A and 12B, the ringconcave groove 24 changes its positions in the radial direction alongthe periphery to make the contact pressure P of the sliding portion 23on the surface of the rotation shaft 20 uneven (ununiform) in theperipheral direction. The lubricant oil is induced from positions of lowcontact pressure (positions corresponding to the arc portions D₃) andspread over the entire periphery of the sliding portion 23 with therotation of the rotation shaft 20, and frictional heat is restricted andearly abrasion is prevented thereby to improve the durability.

Next, each of FIGS. 13A and 13B, corresponding to above-mentioned FIGS.8B and 12B, shows an embodiment respectively. In FIG. 13A, the ringconcave groove 24 is formed into a polygonal configuration such as ahexagon (number of corners may be freely increased and reduced) whenobserved in a direction parallel to the axis L to change positions inradial direction of the concave groove 24, namely, distances from theaxis to points on the concave groove 24 in the peripheral direction.And, in FIG. 13B, the ring concave groove 24 has a concavo-convexconfiguration such as a flower and rounded gear when observed in adirection parallel to the axis L based on the basic circle to smoothlychange positions in radial direction of the concave groove 24, namely,distances from the axis to points on the concave groove 24 in theperipheral direction.

As described above, in the embodiment of FIGS. 13A and 13B, the ringconcave groove 24 has the configuration which changes its positions inthe radial direction along the periphery to make the contact pressure Pof the sliding portion 23 on the surface of the rotation shaft 20 uneven(ununiform) in the peripheral direction. The lubricant oil is inducedfrom positions of low contact pressure (positions middle of sides inFIG. 13A or positions near concave portions in FIG. 13B) and spread overthe entire periphery of the sliding portion (with the rotation of therotation shaft), and early abrasion is prevented thereby to improve thedurability. Number of sides of the polygon in FIG. 13A and number ofconcaves and convexes may be freely increased and decreased.

Next, FIGS. 14A and 14B, corresponding to the above-mentioned FIGS. 8Aand 8B, show further embodiment. That is to say, although the members ofthe same marks in FIG. 14A are similarly constructed to FIG. 8A,following points are different. A solid line shows an arc portion D₅having a small width dimension on the concave groove 24, a broken lineshows an arc portion D₆ having a large width dimension, and the arcportions D₅ and D₆ are disposed in turn with central angles α and β ofabout 60° for example. It is possible to set the number of each of thearc portions D₅ and D₆ 4 or more, α>β, or α<β. In FIG. 14B, the arcportions D₆ of large width dimension are distinguished by hatching.

As described above, in the embodiment of FIGS. 14A and 14B, the widthdimension of the ring concave groove 24 increases and decreases (alongthe periphery) to make the contact pressure P of the sliding portion 23on the surface of the rotation shaft 20 uneven (ununiform) in theperipheral direction. The lubricant oil is induced from positions of lowcontact pressure (positions of the arc portions D₆ of large widthdimension) and spread over the entire periphery of the sliding portion(with the rotation of the rotation shaft), and early abrasion isprevented thereby to improve the durability.

It is also preferable to make a construction in which the abovementioned embodiments (in FIGS. 8A, 8B, and 12A through 14B) arecombined. For example, it is preferable to change the depth and theposition in radial direction of the concave groove 24 together along theperiphery, change the depth and the width dimension of the concavegroove 24 along the periphery, or change the width dimension and theposition in radial direction of the concave groove 24 together along theperiphery (not shown in Figures).

Next, further embodiments shown in FIGS. 15A through 15D addimprovements to the conventional example in FIGS. 9C and 10C to make thecontact pressure P ununiform in the peripheral direction as describedabove in FIGS. 8A, 8B, and 12A through 14B.

In the embodiment shown in a longitudinal cross section of a principalportion of FIG. 15A and a cross section of a principal portion of FIG.15B, basically similar to FIGS. 9C and 10C, a rubber sealing portion 26,having a sliding portion S₀ which contacts the surface of the rotationshaft 20 on an end portion 33 a of a lip 33, is provided, an outer case34 has a pair of inner brims 36 and 37, and the rubber sealing portion26 is unitedly fixed to the outer case 34 by brazing or adhesion.

A back-supporting metal 28 which supports the rubber sealing portion 26from a back face side is L-shaped in cross section, and having acylindrical supporting portion 28 a, supporting the lip 33 of the rubbersealing portion 26 from an inner peripheral face side, and an orthogonalwall portion 28 b at right angles with an axis L. And, cross sectionalconfiguration of the cylindrical supporting portion 28 a is madeununiform to a (basic imaginary) circle in radial direction. That is tosay, the cross-sectional configuration of the cylindrical supportingportion 28 a is formed polygonal as in FIG. 15B to make contact pressureP (on the surface of the rotation shaft 20) of the sliding portion S₀ ofthe lip end portion 33 a ununiform along the periphery. And, FIGS. 15Cand 15D show another embodiment corresponding to FIG. 15B. Thecylindrical supporting portion 28 a is formed as a ring withconcavo-convex undulation in FIG. 15C, and formed as a ring withconcavo-convex stages in FIG. 15D. In any case, the seal is constructedas to make the contact pressure P of the lip end portion 33 a on thesurface of the rotation shaft 20 uneven (ununiform) along the periphery.

The contact pressure P of the sliding portion S₀ is made small oncorners in FIG. 15B, on convex portions in FIG. 15C, and on convex arcportions in FIG. 15D to facilitate inducement (intrusion) of thelubricant oil into the sliding portion S₀ as to spread the lubricant oilover the whole periphery of the sliding portion S₀ along the rotation ofthe rotation shaft 20 to prevent early abrasion and improve durability.Description of the marks 7, 9, 10, 11, etc. in FIGS. 15A through 15D isomitted because they are similar to that in FIGS. 8A and 8B.

Although it is possible to form the ring concave groove 24 of theabove-described embodiments into a circle having uniform depth anduniform width dimension, or form the back-supporting metal into acircle, and form the sliding portion 23 or S₀ itself into a circularshape with concavo-convex undulation (not a circle) to make the contactpressure P on the surface of the rotation shaft 20 uneven (ununiform) inthe peripheral direction when the rotation shaft is inserted, problemsin air tightness are generated in low pressure state of the sealed fluidor unpressurized state.

In the present invention, not restricted to the embodiments above, forexample, the rubber lip portion may be disposed on the low pressure sideindependent from the rubber sealing portion 5, number of the sealelements 7 may be 2 or more, the seal element 7 may be omitted, and theconfiguration of the supporting metal 8, number and configurations ofthe inner cases 9 and 10 and the inner member 11 may be changed.

With the construction of the above-described embodiments in FIGS. 8A, 8B(9A, 9B, 10A, 10B), and 12A through 14B, the contact pressure P isprevented from being excessive and kept at an appropriate value,lubrication state with the rotation shaft 20 is maintained well,abrasion is restricted, and good sealability (tightness) is demonstratedfor a long time because the pressing force in the inner radial directionby the fluid pressure does not work on the sliding portion 23.Especially, the seal is appropriate for sealing high-pressure gas.Further, the dimension of the rotation shaft seal in the axis directioncan be reduced to be compact.

According to the rotation shaft seal of the present invention, thecontact pressure P is prevented from being excessive and kept at anappropriate value, lubrication state with the rotation shaft 20 ismaintained well, abrasion is restricted, and good sealability(tightness) is demonstrated for a long time because the pressing forcein the inner radial direction by the fluid pressure does not work on thesliding portion 23. Especially, the seal is appropriate for sealinghigh-pressure gas. Further, the dimension of the rotation shaft seal inthe axis direction can be reduced to be compact.

The contact pressure P of the sliding portion 23 on the rotation shaft20 is certainly restricted as not to be excessive because the supportingmetal 8 receives the fluid pressure in parallel to the axis L and movesthe rubber in the radial direction. Further, the dimension of therotation shaft seal in the axis direction can be certainly reduced to becompact.

The contact pressure P of the sliding portion 23 on the rotation shaft20 is easily kept at appropriate value to maintain excellent tightness(sealability) for a long time (good durability).

Especially, the abrasion biting into the sliding portion 23 (generatedin the conventional example) is not generated, abrasion uniformlyproceeds, and the tightness (sealability) is maintained for a long timebecause the high stress area concentrates near the concave groove 24(not near the sliding portion 23).

While a certain interference has to be set for corresponding toeccentricity of the rotation shaft and the housing 22 from the axis L ofthe rotation shaft 20, the contact pressure P can be reduced with theinterference for the concave groove 24. And, trackability to theeccentricity is good for flexibility by the concave groove 24.

The contact pressure P is made ununiform in the peripheral direction tomake the lubricant oil intrude between the sliding portion 23 and therotation shaft 20 from the portions of small contact pressure P, spreadthe lubricant oil over the entire periphery of the sliding portion 23along the rotation to prevent frictional heat generation and earlyabrasion, and long life of the seal is obtained. And, there is anadvantage that defection of air tightness is not generated when thesliding portion 23 itself is formed concavo-convex.

Further, in the embodiment of FIGS. 15A through 15D, even if the seal isnot appropriate for high pressure in claim 2, the contact pressure P ismade ununiform in the peripheral direction to make the lubricant oilintrude between the sliding portion 23 and the rotation shaft 20 fromthe portions of small contact pressure P, spread the lubricant oil overthe entire periphery of the sliding portion 23 along the rotation toprevent frictional heat generation and early abrasion, and long life ofthe seal is obtained under considerably high pressure. And, there is anadvantage that defection of air tightness is not generated when thesliding portion 23 itself is formed concavo-convex. And, the product iseasily converted because it is necessary only to replace theconventional back-supporting metal 38 with the back-supporting metal 28of the present invention.

While preferred embodiments of the present invention have been describedin this specification, it is to be understood that the invention isillustrative and not restrictive, because various changes are possiblewithin the spirit and indispensable features.

1. A rotation shaft seal provided with a rubber sealing portion providedwith an axis-orthogonal wall portion having a sliding portion on aninner peripheral edge and an axis-orthogonal supporting metal,supporting the axis-orthogonal wall portion from a low pressure side,comprising a construction in which a ring concave groove is formed on aback face side of the axis-orthogonal wall portion where theaxis-orthogonal wall portion of the rubber sealing portion is pressed tothe supporting metal to absorb flow in an inner radial direction ofrubber compressed by receiving pressure, and at least one of depthdimension, width dimension, and position in radial direction of the ringconcave groove is set to change in a peripheral direction to makecontact pressure of the sliding portion on the rotation shaft ununiformin the peripheral direction.